1. Field of the Invention
The present invention relates generally to the production of composite materials with smooth, pattern-free surfaces. More particularly, the present invention relates to the use of a shrinkage barrier which is placed just under the surface of the composite material to eliminate or substantially reduce the transfer of fabric patterns from the underlying layers to the composite material surface.
2. Description of Related Art
Fiber-reinforced composite materials include one or more layers of fibers which are located in a resin matrix. The fiber patterns in composite materials range from highly uniform woven fabrics to highly disorganized chopped fibers. During fabrication, the fibers are impregnated with resin and cured to form the final composite material. Sufficient resin is used in forming the composite material so that the fibers are totally immersed in the resin matrix.
In many instances, it is desirable to provide composite materials which have a smooth outer surface. For example, a smooth composite material surface is essential for certain tooling components and a smooth surface is highly desirable for items as boat hulls, architectural facia, signage, automotive trim, recreational vehicle components and a wide variety of other items where a smooth surface is desirable for cosmetic and/or aerodynamic or hydrodynamic reasons.
In many instances, the underlying fiber or core pattern is located close to the resin matrix surface. In these instances, it is difficult to keep the underlying fabric pattern from being transferred to the composite material surface. As a result, the underlying pattern is many times visible on the surface of the composite material. This surface pattern is undesirable for cosmetic reasons in many situations and is undesirable from an engineering standpoint when a smooth surface is required.
Many of the resins used in fabricating composite materials tend to shrink during cure. This shrinkage of the resin exacerbates the above-mentioned problem with respect to fiber pattern transfer to the composite material surface. One attempt to solve this problem has involved using low shrinkage resins. However, this approach has met with limited success since the fiber pattern still tend to be transferred to the composite material surface. Further, these resins are generally brittle and have low impact resistance.
Other attempts to limit pattern transfer include extending cure times for the resins in an attempt to reduce shrinkage and adding a layer of syntactic foam next to the outer surface. Also, low profile fibers have been used in attempts to reduce the visibility of the fiber pattern on the surface. These attempts have met with different degrees of success. However, none of these procedures for eliminating fiber patterns from the composite material surface have been entirely successful.
There presently is a need to provide an efficient, cost effective and reliable way to prevent underlying patterns from being transposed to the composite material surface. The resulting composite material should have a surface which is pattern free and extremely smooth. Further, it is important that the smooth composite material surface be obtained without adversely affecting or otherwise compromising the structural integrity and durability of the composite material.